1. Field of the Invention
Embodiments disclosed herein relate generally to delivery systems for ethylene blocking agents. More specifically, embodiments disclosed herein relate to compositions including ethylene blocking agent complexes and water-soluble or water-swellable polymers.
2. Background
Ethylene is an important regulator of the growth and development of plants, interacting with ethylene receptor proteins in plant tissues. In harvested fruits, vegetables, and ornamentals, ethylene may promote color development, ripening, stimulate dehiscence in nuts, promote flowering, and reduce lodging in cereals. Ethylene may also be produced by plants in biologically active amounts in response to various stresses, including drought, chilling, water-logging or flooding, anoxia, and various pathogens. Such stress associated production of ethylene is known to cause programmed cell death leading to the premature death of plants or plant parts, including, for example, flowers, leaves, fruits, and vegetables, through binding with certain ethylene receptors in the plant. Ethylene is also known to cause abscission of leaves and flowers during certain growth and stress conditions, and to promote leaf yellowing and stunted growth as well as premature fruit, flower, and leaf drop. In addition, ethylene is also known to induce or accelerate the ripening of harvested fruits and vegetables, which may result in excessive softening and increased susceptibility to pathogens. Because of these ethylene-induced effects, ways to control the effects of ethylene on plants are sought.
Current methods to control shelf-life of plants, fruits, and vegetables may include ethylene blocking agents (antagonists of ethylene action or its biosynthesis), as will be described in more detail below. Additionally, methods to control shelf-life that may be used in place of or in combination with ethylene antagonism include harvesting before peak ripeness, treating with inhibitors of membrane degrading phospholipases, (e.g., hexanal and lysophosphatidylethanolamine) cold storage, modified atmosphere packaging, packaging materials that minimize bruising, wax coatings on the product or packaging, ethylene scavengers, ethylene exposure to promote ripening, and direct genetic modification of the organism, among others.
U.S. Pat. No. 5,518,988 discloses the use of cyclopropene and its derivatives, including methylcyclopropene, as effective blocking agents for ethylene binding. However, a major problem with these compounds is that they are typically unstable gases which present explosive hazards when compressed.
U.S. Pat. No. 6,017,849 and EP1237411 disclose incorporation of these gaseous cyclopropenes into a molecular encapsulation agent complex in order to stabilize their reactivity and thereby provide a convenient and safe means of storing, transporting, and applying or delivering the active compounds to plants, avoiding the problems presented by the unstable gases. For the most effective cyclopropene derivative disclosed in U.S. Pat. No. 5,518,988, 1-methylcyclopropene (“1-MCP”), the preferred molecular encapsulation agent is a cyclodextrin, with alpha-cyclodextrin being the most preferred. The encapsulation of 1-MCP improves the stability of the product during transportation and storage by allowing the 1-MCP to be delivered in a powdered form and later activated by contacting the complex with gaseous or liquid water to release the 1-MCP gas. Thus, the application or delivery of these active compounds to plants is accomplished by simply adding water to the molecular encapsulation agent complex.
U.S. Pat. No. 6,313,068 discloses the encapsulation of longer chain cyclopropene derivatives in cyclodextrin, among other encapsulation agents. Also disclosed is the packaging of the 1-MCP complex, where the preferred package is made of polyvinyl alcohol. When the consumer is ready to use the complex, the consumer may dissolve the powder and the packet in an aqueous solution and expose the resulting solution to the plant.
U.S. Pat. No. 6,444,619 and EP1192859 indicate that the powder formulations suffer from a number of deficiencies including, for example, dustiness, difficulty in measuring small amounts (which may require that the material be prepackaged), and difficulty in controlling the release of the encapsulated material from the powder, and that it would be advantageous to moderate the release of 1-MCP so that very little of it is released during the first few minutes after the complex is added to water. To overcome these deficiencies and to moderate the release of 1-MCP, U.S. Pat. No. 6,444,619 and EP1192859 disclose that the encapsulated 1-MCP may be pressure agglomerated to form tablets, wafers, pellets, briquettes, and similar forms.
U.S. Pat. No. 6,897,185 and WO2002024171 disclose the addition of an effervescent agent with a tablet form of the 1-MCP complex to speed the release of 1-MCP upon exposure to moisture. The effervescent action may facilitate the bursting of the tablet in an aqueous solvent, thereby promoting the release of 1-MCP. U.S. Pat. No. 6,762,153 and EP1304035 disclose improving the efficiency of the 1-MCP release by combining the 1-MCP complex with one or more carbon dioxide generating additives (a combination of acids and carbonates or bicarbonates, such as a combination of citric acid, sodium bicarbonate, and benzoic acid).
U.S. Patent Application Publication No. 2003220201 discloses a method for delivering cyclopropene gas to plants in an enclosed space. The delivery method comprises bubbling gas through a volume of water that contains a suspension of a cyclopropene/cyclodextrin complex. The bubbling action may provide the energy to liberate the cyclopropene from its carrier molecule and then facilitate transit of the cyclopropene from the water into the atmosphere.
U.S. Pat. No. 6,426,319 and EP1192858 disclose incorporation of a super-absorbent polymer (SAP) to the 1-MCP/cyclodextrin complex. The SAP may provide for a slow release of the cyclopropene from the encapsulating agent or may provide for release of the cyclopropene with only small amounts of water.
U.S. Pat. No. 6,548,448 and EP1236397 disclose incorporation of a cyclopropene derivative compound with a packaging material. The packaging materials may include cardboard and plastic containers, wooden boxes, paper bags, wax coatings, coated paper, plastic films, and adhesives. Plastic film compositions include polyethylene, ethyl vinyl acetate polymers, polyvinyl alcohol, and polystyrene. The packaging materials included either (a) a sachet/packet within which the 1-MCP complex was heat sealed, or (b) films exposed to 1-MCP vapor. When the 1-MCP was in the form of a complex, the 1-MCP was released by exposure to humidity, and when the 1-MCP was not in the form of a complex, the 1-MCP was released by simple diffusion.
WO2004101668 discloses a packaging film composition comprising a thermoplastic base, a filler, an ethylene response inhibitor, and a moisture transmitting material. The ethylene antagonist incorporated in the thermoplastic film is released via moisture from a plant contained in the package. The thermoplastic bases described include polyolefins, polycarbonates, polyamides, ethyl vinyl acetate and ethyl methyl acetate copolymers, and polysulfones, among others. Calcium carbonate was used as the filler, and polyethylene glycol was used as the moisture transmitting material.
U.S. Pat. No. 6,770,600 and EP1340425 disclose delivery substrates for the 1-MCP complex that can be plastic, paper, or fabric from natural or synthetic fibers. The release agent can be a gel, such as hydroxypropylmethylcellulose or polyvinylpyrrolidinone, coated onto paper, polypropylene, polyester, or polyethylene non-wovens or films. Water contact with the gel causes the release of 1-MCP which permeates through the porous substrate. The 1-MCP/cyclodextrin complex may be incorporated into hydrophilic gels applied as coatings, such as a tape. The tape may be pulled through a water chamber or exposed to moisture to release the 1-MCP. The hydrophilic gels of U.S. Pat. No. 6,770,600 and EP1340425 are applied as coatings to a non-soluble substrate, not to films that would dissolve upon exposure to sufficient water.
Other delivery methods include two-compartment systems, where water is provided in one compartment and the 1-MCP complex in the other. Upon breach of the separation between the two compartments, the contents mix to activate and release the 1-MCP.
The above described powders, tablets, and films may present handling issues, and may be slow to dissolve or may not controllably release the 1-MCP. Accordingly, there exists a need for more convenient, effective, and efficient ways to release and deliver 1-MCP.